This invention relates to systems for polishing semiconductor wafers and other substrates.
In many areas of technology it is necessary to polish a substrate to a high degree of planarity. For example, in the manufacture of integrated circuit chips, a semiconductor wafer having thin films of a dielectric or metal deposited on it must be polished to provide a planar surface on which further processing can be performed. The substrates used in the manufacture of data storage disks must also be polished.
Chemical-mechanical polishing (CMP) is a known technique for polishing substrates. In the most common CMP systems the substrates are rotated while an abrasive slurry is introduced between the surface to be polished and a polishing pad. Grains of the abrasive slurry are trapped between the surface and the polishing pad, and the relative movement between the surface and the polishing pad causes the grains to impact and wear down the surface. A problem with slurry systems is that the grains impact both xe2x80x9cpeaksxe2x80x9d and xe2x80x9cvalleysxe2x80x9d of the surface, and this limits the ability of the system to planarize the surface. Also, the substrates are exposed to different conditions as the polishing pad wears out, and this has an adverse effect on the uniformity of the polished substrates. Other problems are xe2x80x9cdishingxe2x80x9d erosion of the substrates, which are inherent in a slurry polishing process.
More recently, so-called xe2x80x9cfixed abrasivexe2x80x9d systems have come into use. In these systems, the abrasive grains are adhered to a film (roughly in the manner of ordinary sandpaper) and the surface to be planarized and the fixed abrasive are moved relative to one another. In the Obsidian Flatland(trademark) 501 polisher marketed by Applied Materials, Inc., the substrate is held on a carrier and pressed downward onto the fixed abrasive. The carrier is moved in an orbital pattern against the abrasive. The abrasive is provided in a roll-to-roll form and is stepped forward periodically so that each wafer is exposed to a polishing surface with a similar wear pattern. This helps to overcome the non-uniformity problem mentioned above.
Despite the improvements that have been made, there still exists a need for a polishing system that efficiently polishes substrates to a high degree of planarity and provides a high degree of uniformity, both as to a given substrate and across a batch of substrates.
A substrate polishing system according to this invention comprises a first drum and a second drum rotatable about parallel axes. At least one reciprocating motor is used to rotate the first and second drums in a reciprocating manner. The system also includes a platen having a bearing surface and an abrasive tape extending from a supply roller to a takeup roller. The supply roller is mounted inside the first drum, and the takeup roller is mounted inside the second drum. The supply and takeup rollers have axes that are parallel to (or may coincide with) the axes of the first and second drums. The abrasive tape extends through an opening in the first drum, over the bearing surface, and through an opening in the second drum. At least one indexing motor is used to rotate at least one of the supply and takeup rollers in a given direction. A substrate carrier is used to press a substrate against the abrasive tape in a region adjacent the bearing surface.
In one embodiment separate reciprocating motors drive the drums and separate indexing motors drive the supply and takeup rollers.
The substrate is polished as the reciprocating motors drive the drums and cause the abrasive tape to move back and forth between the substrate and the bearing surface of the platen. After a substrate has been polished, the indexing motors advance the tape a preselected distance from the supply roller to the takeup roller. Then a second substrate is polished and the tape is advanced by the preselected distance again. In this way, after several substrates have be processed, each successive substrate is exposed to a section of the abrasive tape that has be worn to the same degree. Therefore, the polishing of successive substrates is highly uniform.
This invention also includes a method of polishing a substrate comprising pressing the substrate against an abrasive tape; reciprocating the abrasive tape; and advancing the abrasive tape periodically and incrementally in a first direction.